Conformation and Orientation of Gramicidin a in Oriented Phospholipid Bilayers Measured by Solid State Carbon-13 NMR

Abstract

Three analogues of the helical ionophore gramicidin A have been synthesized with 13C-labeled carbonyls (13C=O) incorporated at either Gly2, Ala3, or Val7. A fourth compound incorporated 13C at both the carbonyl and α-carbon of Gly2 within the same molecule. These labels were studied using solid-state, proton-enhanced, 13C nuclear magnetic resonance (NMR) in hydrated dispersions of dimyristoylphosphatidylcholine (DMPC)-gramicidin A. The dispersions were aligned on glass coverslips whose orientation to the magnetic field could be varied through 180°. The orientation dependence of the NMR spectrum was used to obtain an accurate measurement of the 13C chemical shift anisotropy (CSA), and in the ..